The present invention relates to video compression and decompression, and more particularly to filtering in block-based methods.
Digital video compression allows for practical (reduced bandwidth) realtime transmission of video without significant loss of quality. Many video compression standards have been developed beginning in the 1980s and include H.261, H.263, MPEG-1, MPEG-2, MPEG-4, and so forth. These standards generally use a block-based compression which includes motion compensation, block transform (e.g., DCT or wavelet) coding, and quantization. FIG. 2 illustrates a system with motion estimation (ME), motion compensation (MC), DCT, quantization (Q), inverse DCT (IDCT), and variable length coding (VLC) of the transmitted motion vectors and quantized DCT-transformed motion compensation residual.
H.264 is a new video compression video standard being developed by ITU-T. It offers much higher coding efficiency which provides about 30–50% additional bit-rate reduction at the same coding qualities as compared to the MPEG-4 SP. A typical application of H.264 could be wireless video on demand, in which the bandwidth is so limited that a coding standard of high compression ratio is strongly desired.
The basic coding techniques in H.264 are still the motion compensated prediction, transform, quantization and entropy coding. However, it differs from MPEG-4/H.263 in great detail. One of major differences lies in the transform and quantization. Instead of 8×8 DCT transforms, H.264 uses a 4×4 integer transforms for the residual coding (residual blocks are generated by using the motion compensation for inter-coded macroblocks, and using the intra prediction for intra-coded macroblocks).
As with all block-based compression methods, H.264 suffers from blockiness in the decompressed (reconstructed) video images. FIG. 3 illustrates the edges of blocks (4×4 blocks within 16×16 macroblocks) subject to deblocking filtering.